Method of and means for coupling two high frequency circuits



Oct- 1939. w. VAN B. ROBERTS 2,175,363

METHOD OF AND MEANS FOR COUPLING TWO HIGH FREQUENCY CIRCUITS Filed Jan.7, 1938 y- &9- 2

N r L -----------l Y 5 i i l I F !v a H. F. H. E TRANSLAT/NG TRANSLAT/NGA PPA PA 71/5 APPARA TUS H E H. E v

TRANSLATING TRANSLAT/NG APPARATUS APPARATUS INVEN TOR. WAL TER VAN B.ROBERB BY 71 MZ ATTORNEY.

iatented Oct. 10, 1939 2,175,363 7 METHOD OF AND MEANS FOR- C'OUPLINGTWO HIGH FREQUENCY GIRC-UIT' S- Walter van B. Roberts, Princeton, N. J.,assignor to Radio Corporation of of Delaware America, a corporationApplication January 7, 1938, Serial No. 183,783

10 Claims.

The present invention relates to improvements in the method of and meansfor coupling together two high frequency circuits, and particularly to amethod of and means for coupling a transmission line to an antenna.

' A general object of the present invention is to provide an improvedcoupling means between a transmission line or other circuit, and asecond circuit composed at least in part of a hollow conductor.

A more specific object of the invention is to provide a coupling betweencircuits of the type referred to above, which coupling is free ofmetallic contacts.

A further object of the invention is to provide both a coupling and animpedance matching device for transmitting energy from one alternatingcurrent circuit to another, without a metallic contact between thecircuits.

A known method of coupling two high frequency circuits is shown in Fig.1, which shows a transmission line TL connected to a dipole antenna A.In such a known arrangement it has been found that where a dipole ismade of 25 aluminum there is difficulty in making a reliable lowresistance contact from the transmission line to the dipole antenna,without interfering with the current flow along the outer surface of thedipole antenna. 30 The present invention overcomes the foregoingdiificulty, among others, by enablingcou- .pling to be effected betweenthe dipole antenna and the transmission line without utilizing anymetallic contact at all between the two circuits. 35 A more detaileddescription of the invention follows in conjunction with the drawing,wherein: Fig. 1 illustrates a known type of coupling arrangement betweenan antenna and a transmission line, while 40 Figs. 2, 3, and 4illustrate several embodiments of the present invention given by way ofexample only, in order to illustrate the principles involved.

As mentioned above, Fig. 1 illustrates prior practice wherein atransmission line TL extending from suitable high frequency transmittingor receiving apparatus, shown conventionally in box form, connects withan antenna A by direct metallic connection at two spaced points H, H 50on the antenna. These points are so spaced that the impedance of thetransmission line TL is approximately matched by the load impedance intowhich it works.

.A further difiiculty which the known system of Fig. 1 experiences liesin the fact that the spacing between the junction points of the antennaA and the transmission line TL may not be such that there is obtained asufiiciently good impedance match between the two circuits at theterminals of the transmission line so as to avoid standing waves on thetransmission line.

This difficulty is overcome, in accordance with a another embodiment ofthe invention, by providing a matching section of transmission linewhich is addedto the contactless coupling arrangement, while stillmaintaining a complete lack of metallic contacts between the variousparts of the system.

. In Fig. 2, illustrating one embodiment of the present invention, thedipole antenna A consists, at least in that-part thereof between thecoupling points H, H, of a hollow conductor, and the transmission lineTL is brought through 'the hollow portion of the tubular antenna Abetween theholes H, H at positions correspond-' ing substantially to thepositions at which contacts would be made if the contacts were to beused in the manner shown in Fig. 1. As shown in the drawing, thetransmission line TL is spaced or insulated from the antenna A in suchman-:

ner that there is no direct metallic connection between the transmissionline and the antenna either at the holes H, H or throughout the lengthof the portion of the transmission line within the hollow dipole. Themutual inductance be-' tween the antenna A and the transmission linecircuit TL is exactly the same as if the wires ofthe line weremetallically connected to the antenna A at the points where thetransmission line wires enter the holes H, H, in the antenna.

Fig. 3 shows a modification wherein an impedance matching section iseifectively added to the contactless coupling arrangement of Fig. 2. Inthis figure, there is shown a tubular antenna A which is coupled withoutmetallic contacts to a tubular conductor T of smaller diameter, whichconductor T is bent around so that the end portions E thereof lieparallel to each other so as to form a matching section M. This matchingsection M of the tubular conductor T is continuous with the couplingportion extending through the holes H, H of the antenna, and has alength and spacing which is determined in accordance with the inputimpedance of the coupling portion. Effectively, we thus have a matchingsection of line inserted between the transmission line TL proper and theterminals P, P whose impedance is to be matched to that of theline. Bysuitable choice of the length and characteristic impedance of thematching sec-' tion M of tubular conductor T, the complex load presentedat points P, P of the antenna coupler T is transformed into a pureresistance equal to the characteristic-impedance of the transmissionline TL. The separation between .the conductors E, E of the matchingsection M and the length thereof are determined in part'by the impedancemeasured at the points P, P where the matching section M changes intothe coupling loop or triangular portion of tube T which provides thedesired mutual inductance with the antenna. The length and spacing ofthe matching section M is determined for the rest by the characteristicimpedance of the main transmission line. A

more detailed description of the manner in which this matching sectionfunctions to transform the complex load of the antenna into a pureresistance equal to the characteristic impedance of the transmissionline proper is described in more detail in my copending application,Serial No. 162,302, filed September 3, 1937, to which reference is heremade.

Although it is possible to connect the transmission line TL metallicallyto the ends of the matching section .M remote from the antenna A, inaccordance with the present invention, such .metallic contact is avoidedby passing .the transmission line TL through the entire tubularconductor T which acts both as a coupling loop and .a matching section.It should be noted in Fig.

3, that the transmission line 'IL makes no direct metallic connectionwith the .tubular conductor T, and the tubular conductor T in turn makesno direct metallic connection with the antenna A. For this purpose, ifdesired, insulators may be provided between the conductors of the .lineTL and the tubular .conductor II, and also between the tubular conductorTand theantenna A, thus insuring the avoidance of all .metallic contactswhich are subject to corrosion. This insulation need .not be of highquality, since littlepotential difierenceexists thereacross.

.Fig. 4 illustrates a further modification -of the invention,wherein'the coupling .member T (triangular shapedoircuit) :is made ofhollow tubing of larger diameter than the dipole antenna A", the antenna.being .passed through a. portion of the coupling member.

One advantage of providing .insulationbetween the wires of thetransmission line TL and the antenna A of Fig. .2,.and;between various:conductors of the system of Fig. 3, is that there is avoided variableand sporadic contacts which may cause electrical disturbances :inthesystem.

What is claimed is:

1. .In combination, an antenna having a hollow portion in the interiorthereof communicating with the exterior througha pair of spacedapertures located intermediate the ends of said antenna, a continuoushollow conductor extending in theinterior of said hollow .portion andemerging through said apertures, .said ghollow conductor beinginsulatinglyarranged with respect to said antenna, and a transmissionline coupled to said hollow conductor.

2. In combinatioman antenna havingahollow portion in the interiorthereof communicating with the exterior through a pair of spacedapertures, a continuous hollow conductor extending in the interior ofsaid hollow portion and emerging through said apertures,said, hollowconductor being insulatingly arranged with respect to said antenna, anda transmission line passing through the interior of said hollowconductor.

3. In combination, an antenna having ahollow portion in the interiorthereof communicating with the exterior through a pair of spacedapertures, a continuous hollow conductor extending in the interior ofsaid hollow portion and emerging through said apertures, said hollowconductor being insulatingly arranged with respect to said antenna, anda'transmission .line passing through the interior of said hollowconductor and insulated therefrom.

4. In combination, an antenna having a hollow portion in the interiorthereof communicating with the exterior through a pair of spacedapertures, a continuous hollow conductor extending in the interior ofsaid hollow portion and emerging through said apertures, said hollowconductor being insulatingly arranged with respect to said antenna, andhaving end portions extending parallel to each other, a transmissionline coupled to said end portions, said end portions having such lengthand being so spaced that the complex load of said antenna is transformedinto a pure resistance equal to the characteristic impedance of thetransmission line.

5. In combination, an antenna having a hollow portion in the interiorthereof communicating with the exterior through a pair ,ofspacedapertures located intermediate the ends of said antenna, and atransmission line having a pair of conductors extending through saidapertures and joined together in the interior of said antenna to form acontinuous conductor, said line being insulatingly arranged with respectto ,Said ,antenna to prevent ,metallic contact therebetween.

6. .In combination, an antenna having a hollow portion in the interiorthereof communicating with the exterior through a pair of spacedapertures, and a transmission line having a pair of conductors extendingthrough said apertures and joined together in the interior of saidantenna to form a continuous conductor, saidline being ;in-

sulatingly arranged with respecttosaid antenna to prevent metalliccontact therebetween, said apertures beingyso spacedthat standing waveson the transmission line are rendered negligible.

,7, In combination, an aerial element, and a feeder element coupled tosaid aerial at points intermediatethe ends of said aerial, said feederelement being in the :form of a loop, one ofsaid elementsbeing ,hollowfor at ;least part of .its length for accommodatingthe other elementtherein, said elements being insulated from .each other.

the form of aconducting loop.coupled to .said aerial at a locationintermediate theendsofsaid aerial, a portion of said loop being :hollowfor accommodating an intermediate portion ofsaid aerial, and highfrequency translating apparatus coupled to the ends of said loop.

9. In combination, a dipole antenna which is effective as a radiatorthroughout its .entire length,,said dipole having ahollowportionintermediate the ends thereof, atwoeconductorfeeder'havingits circuit completed through said hollow portion butinsulatingly arranged with respect to said dipole antenna, andhighfrequency translating apparatus .coupledto the two conductors of saidfeeder.

10. In combination, an antenna .havingahollow portion in the'interiorthereof communicating with the exterior through a pair of spacedapertures locatedlintermediate the .ends of said,

antenna, and a continuous conductor loop passing through said apertures,the portions of ,said loop external of said apertures being brought intoparallelism to form a parallel wire transmission 8. Ingcombination, anaerial anda feeder in

